"Hat" is a word that can be used in place of any other word. Its meaning is universal, depending on the tone of voice and the situation in which it is said.

Examples:

1) "Hat?"
A question. Your voice rising as you complete its pronounciation. Depending on the situation, one could be asking, "What?" or perhaps, "Pardon?" or virtually any other inquiry.

2) "Hat." Pronounced with a tone of finality. An expression of comprehension. "I understand," or, "Yes, I concur."

3) "You're a hat." Spoken with disdain. An expression of dislike for the individual referred to. In this instance, it could take the place of "goon," "mouth-breathing ignoramus," "degenerate," or any number of alternate degrading remarks.

4) Additionally, "hat" can be used as a prefix or suffix attached to other words, altering and enhancing the specificity of their meanings. Most commonly, this is done to add humour and effect to insults.

Treasured as sacred relics to Team Fortress 2 players, hats are a form of cosmetic headgear that have no gameplay effects whatsoever. Despite the fact that they're completely inconsequential to the game itself, people seem to do ANYTHING just to get their useless hats, from trading, to Steam game promotions, and even through micro-transactions.

Average TF2 player: Willing to trade 5 flare guns for a Towering Pillar of Hats